Exclusive breastfeeding of newborn babies is recommended up to 6 months of age by the World Health Organisation, with continued breastfeeding along with appropriate complementary foods up to two years of age or beyond. It is very important that the mother can produce an appropriate amount of milk for her baby to feed on. This requires good control of the supply-and-demand relationship because the mother's breasts will act to match the amount of milk produced depending on how much the baby feeds.
When a good supply-and-demand relationship is established, the mother's milk supply is matched to the baby's demand. So a normal breastfeeding session will end when the baby has had enough milk. Some mothers choose to express milk with a breast pump when they cannot feed their babies directly or it is inconvenient to do so.
When using a breast pump, it is difficult for the mother to know how much milk remains in her breast and when to stop using the breast pump. It is important to know whether all the milk has been expressed from the breast because, according to lactation physiology, if the breast is not emptied, long term milk production will decrease as the breast acts to balance the supply-and-demand relationship. Furthermore, mastitis may occur if milk remains in the breasts too long, since it creates a good environment for bacterial growth.
It is known that a mother can monitor how much milk is produced and match this to the baby's needs. However, this can be difficult, especially as the baby grows and requires more milk, and the breasts may be caused to produce more or less milk than required.
It is also known, for example from WO 2001/054488 A1, to use flow meters to monitor the rate at which milk is being expressed by a breast pump. This can be used to give an indication of the emptiness of the breasts; the rate will decrease as the breasts empty. However, this may be inaccurate and could confuse breast pump equipment malfunction (such as blockages or loss of vacuum seal) with an empty or almost empty breast.
It is also known, from WO 2009/060448 A2 and US 2005/0059928 A1, to use electronic sensors to monitor the breast during pumping or feeding; the breast's shape, electrical conductivity and other characteristics can give an indication of the fullness of the breasts. Again, this can be inaccurate and is difficult to calibrate for different users.
Furthermore, the methods and devices mentioned above are inconvenient to use and are often bulky and uncomfortable because of the required sensors that are attached in the breast area.
The constitution of milk varies for people, at different lactation stages and even during one breastfeeding. Generally speaking, breast milk is a solution with 87%˜88% water, ˜4% fat, ˜7% lactose and ˜1% protein and other minerals. The fat is insoluble in water and so takes the form of fat globules suspended in the water. The fat globules have an average diameter of 4 μm. These are the largest particles present in breast milk. Proteins, such as casein protein, are also present in particle form, but much smaller 0.005 μm-0.3 μm. Other constituents of the breast milk are dissolved in the water and so have no significant particle presence.
It is known that as a breast empties, the fat content of the breast milk rises. The difference in fat content during a breast feeding session can range from 20 gram/liter in foremilk to 130 gram/liter in hindmilk. Typically, scientists use this measure as an accurate and reliable way to determine the amount of milk, if any, remaining in a breast. To determine the fat content of a milk sample, a centrifuge is commonly used to separate the fat (which is insoluble) from the water. The quantity of fat can then be measured.
Another method of determining when a breast is empty is to estimate the breast volume using a breast imaging technique. The shape of the breasts will naturally change as they are emptied and this is a difference visible from the exterior.
Neither the centrifuge nor the breast imaging methods are suitable for regular, everyday use as they require equipment and processes that are complex, costly and inconvenient and which cannot be carried out quickly and easily in real time and on a sample of milk that has only just been expressed from the breast and whilst the breast pump is still in use.
Therefore, there is a need for a method that will quickly and easily provide an indication as to the amount of milk remaining in a breast during lactation, without compromising the function of the breast pump or the comfort and convenience of the user.